A conventional crystal oscillation circuit obtains oscillation output by coupling a crystal oscillator, a feedback resistive element, and a capacitative element between an input terminal and an output terminal of an inverter including a P-channel MOS (Metal-Oxide Semiconductor) transistor and an N-channel MOS transistor. The crystal oscillation circuit has a problem that it takes time until the oscillation frequency and the amplitude level are stabilized.
Regarding this problem, for example, a crystal oscillation circuit described in Japanese Patent Laying-Open No. 59-91709 (Patent Document 1) is known. This oscillation circuit has two sets of crystal oscillation circuits sharing one crystal oscillator, and is configured such that the crystal oscillator vibrated by one crystal oscillation circuit is switchingly connected to the other crystal oscillation circuit and operated.